1. Field of the invention
The present invention concerns grinding machines including a grinding wheel support shaft and a pattern support shaft coplanar with the grinding wheel support shaft carried by a box member adapted to pivot relative to the grinding wheel support shaft, the end of the pattern support shaft overlying a bearing key adapted to support a pattern attached to the pattern support shaft.
Grinding machines of this type are used among other things for trimming ophthalmic lenses to be fitted to eyeglass frames.
2. Description of the Prior Art
The usual method employed at present for trimming an eyeglass lens is to attach to the pattern support shaft of a grinding machine of this kind, in line with the corresponding bearing key, a pattern the contour of which is identical to that of the ring or surround of the eyeglass frame concerned while the eyeglass lens itself is attached to the pattern support shaft, or to a shaft constrained to rotate with it, in line with a grinding wheel carried by the grinding wheel support shaft.
The engagement of the eyeglass lens with the grinding wheel and therefore the trimming of the lens continue of themselves until, in the relevant angular position of the pattern support shaft, the pattern carried by the latter shaft comes into contact with the bearing key provided for this purpose and it then remains only to rotate the pattern support shaft on itself to bring about progressively the required trimming.
This trimming is effected by copying and is therefore equivalent to conjugating with the angle .alpha. by which the pattern support shaft has rotated on itself relative to a reference a specific distance D between the pattern support axis and the grinding wheel support axis.
There have been proposed grinding machines in which this conjugation of the distance D with the angle .alpha. is effected directly using a contour following device adapted to obtain the corresponding geometrical data from the eyeglass frame concerned without any material pattern being produced between this measuring and the trimming.
This is the case, for example, with the grinding machine briefly described in French patent No 2 481 635.
In practice, it is just as if a pattern simulator were integrated into the grinding machine to drive it directly from the measurements made by a contour following device, the pattern that it provides being, at most, merely shown by a plot on a screen.
A grinding machine of this kind is inevitably relatively complex and therefore costly and does not enable use of a real pattern in cases where a pattern is already available.
Its characteristic feature also means that the advantages of a pattern simulator cannot be obtained with grinding machines not originally provided with one.
U.S. Pat. No. 3,688,642 describes a pattern simulator comprising a stylus adapted to be deflected under the control of a member movable along X, Y, Z axes while the machine concerned includes a detector responsive to deflection of the stylus. Assuming such a thing were possible, no combination of this document with the previous document would make it possible to confer the advantages of a pattern simulator on grinding machines not initially provided with same.
A general object of the present invention is to provide a pattern simulator that has the advantage of being usable on any existing grinding machine of this kind.